This invention relates to a mechanical face seal assembly for rotating shaft assemblies which is less expensive than known seals.
Mechanical face seals are commonly used to prevent gases and liquids from leaking along rotating shaft assemblies. The seal must be capable of sealing the shaft both statically and dynamically. That is, both when the shaft is rotating and when it is stopped. Further, the seal is required to withstand high operating pressures, temperatures and shaft speeds. Mechanical face seals provide longer life and less leakage than radial lip seals. Face seals are used in pumps due to their ability to withstand large changes in pressure. This type seal is also compatible with many fluids.
Typically a face seal is provided between a rotating shaft and a fixed housing. In known face seals a seal ring is fixed to a housing wall. A spring biased washer rotates with the shaft and is biased toward the seal ring. The washer and spring must be carefully balanced, since they rotate. The primary sealing effect takes place at opposed faces of the washer and seal ring. Secondary sealing elements are often necessary to augment the primary seal.
Known mechanical face seals often fail because the secondary seal between the shaft and the washer wears down due to vibration and shaft galling caused by abrasive particles in the fluid. Therefore, the seal has to be replaced. Replacement is costly and time consuming. It is common for the secondary seal to be replaced as often as once a month. More recently, in some applications mechanical face seals can last about 0.5 million miles (i.e., approximately the lifetime of a truck). However, these long lived seals are very expensive.
Therefore, a major concern is reducing the cost of a long-lived face seal. One main factor influencing the cost of the seal is due to the rotating washer and the need to balance the spring and the washer. The process of balancing the spring and the washer is difficult.
Further, the known rotating washer does not permit a compact mechanical face seal. The prior art fails to address the need to produce a mechanical face seal that is less costly.
Accordingly there remains a need for a mechanical face seal that can be fabricated easily and economically.